This invention relates to injection molding apparatus and, in particular, to an injection molding machine having a removable liner or liners positioned between the clamping and support plates of a mold base assembly to permit economic molding of a limited number of parts.
As is well known in the injection molding art, a mold base having two separable halves is typically mounted in an automatic machine which, among other things, delivers a molten material to the base assembly. The material typically is plastic but can be metal. The base assembly generally includes a clamping plate and an opposing support plate that are moved by actuators between an open and a closed position. A molding cavity is cut or otherwise formed in the opposing surfaces of the two plates which replicates the part to be molded.
When molding a part, the mold is closed and the molten material is delivered to the mold cavity by a sprue system to fill the cavity. The base assembly is typically provided with a cooling system which rapidly cools the part so that it can be removed from the assembly. Upon cooling, the assembly is opened and ejector pins brought into contact with the part to remove it from the mold cavity.
It has heretofore been the practice in the art to have a highly-skilled mold maker cut the mold cavity in one or both opposing plate surfaces of the base assembly. This typically is a time consuming and expensive procedure which renders the base assembly unusable except in the manufacture of a specific part or parts. When the part is discontinued or no longer needed, the entire base assembly is usually scrapped. As a consequence, it has been found uneconomical to injection mold parts where the quantity required is relatively small.
The lead time required to produce a finished base assembly that is ready for use in a molding machine is also relatively long. Lead times are generally in the nature of weeks and even months. Only those who mass produce the parts over a long period of time can afford this kind of delay. Others, however, usually adopt more costly but faster fabricating methods.